An engine of a vehicle may be automatically stopped during select conditions to conserve fuel. The engine may be restarted during other conditions when it is desirable to move the vehicle. Some vehicles that are automatically stopped may include an automatic transmission. The transmission may be in a selected gear at the time the engine is stopped. If the vehicle is stopped on a downhill grade and the engine is automatically restarted while a gear is engaged, the vehicle driveline lash may initially increase, due to an increase in gear tooth to tooth spacing or a loss of tension in a chain drive, due to the negative grade. The increased lash may be taken up suddenly and a tooth to tooth, or chain link, impact load may occur after the engine is restarted. The impact load between gear teeth or within a chain drive may provide an undesirable audible sound as well as gear tooth or chain drive degradation.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for starting an engine, comprising: automatically starting the engine; and holding a vehicle brake in response to a road grade after a vehicle brake pedal that operates the vehicle brake is released.
By holding vehicle brakes in an applied state in response to a road grade, it may be possible to reduce the possibility of impact loads between gear teeth or within chain drives when the engine is restarted and positive torque is applied to the driveline. For example, if road grade is zero, vehicle brakes may be released when a driver releases a brake pedal. On the other hand, if the road grade is non-zero and negative, the vehicle brakes may be released after engine speed reaches a threshold speed where a torque converter transfers positive torque to the driveline. Holding the vehicle brakes in an applied state limits the possibility of increasing gear lash or reducing chain tension in the driveline.
The present description may provide several advantages. In particular, the approach may reduce audible driveline noise. Additionally, the approach may reduce driveline degradation. Further, the approach may improve vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.